Microtome knife sharpening machine

ABSTRACT

A microtome knife sharpening machine comprises a grinding wheel and a microtome knife carrying assembly which is pivotally supported on a support in a manner such that a microtome knife held by the carrying assembly may be swung toward and away from the grinding surface of the grinding wheel. The support has a rod extending outwardly from the support and constituting a pivot shaft of said carrying assembly, which pivot shaft is rigidly connected with the carrying assembly so that when the rod is manually turned the carrying assembly is swung. The rod is enclosed in a sleeve which is slidable relative to the rod but is unable to rotate relative to the same. The sleeve is urged axially inward by a spring and has a radial arm formed with an engaging peg, which is engageable selectively with one of a plurality of engaging depressions formed in the support so that by pulling the sleeve axially outwardly, and thereafter turning and releasing the same, the microtome knife carrier assembly can be locked in one of a plurality of angular positions with respect to its pivot axis.

United States Patent [191 Miyamoto 1 1 June 17, 1975 1 MICROTOME KNIFE SHARPENING MACHINE [76] Inventor: Naomichi Miyamoto, 75-5,

Oaza-lmojiya, Koshoku-shi,

Nagano-ken, Japan [22] Filed: Aug. 14, 1974 [21] Appl. No.: 497,502

[30] Foreign Application Priority Data Aug. 15, 1973 Japan 48-95876 Aug. 15, 1973 Japan 48-95877 [56] References Cited UNlTED STATES PATENTS 1,956,686 5/1934 Kane 51/1255 2,257,354 9/1941 Strezoff 51/1255 2,798,339 7/1957 Hawkins 51/54 3,751,885 8/1973 Pinat............. 51/56 3,844,067 10/1974 Guerra et a1. 51/109 BS Primary Examiner-Othell M. Simpson Attorney, Agent, or Firm-Eric H. Waters [57] ABSTRACT A microtome knife sharpening machine comprises a grinding wheel and a microtome knife carrying assembly which is pivotally supported on a support in a manner such that a microtome knife held by the carrying assembly may be swung toward and away from the grinding surface of the grinding wheel. The support has a rod extending outwardly from the support and constituting a pivot shaft of said carrying assembly, which pivot shaft is rigidly connected with the carrying assembly so that when the rod is manually turned the carrying assembly is swung. The rod is enclosed in a sleeve which is slidable relative to the rod but is unable to rotate relative to the same. The sleeve is urged axially inward by a spring and has a radial arm formed with an engaging peg, which is engageable selectively with one of a plurality of engaging depressions formed in the support so that by pulling the sleeve axially outwardly, and thereafter turning and releasing the same, the microtome knife carrier assembly can be locked in one of a plurality of angular positions with respect to its pivot axis.

PATENTEDJUN 17 192s SHEET 2 7 I111 III-" 1 14111110 PATENTED 17 SHEET 3 FIG. 7

MICROTOME KNIFE SHARPENING MACHINE BACKGROUND OF THE INVENTION The present invention relates in general to grinding machines, and more particularly to a machine adapted to grind knives of a microtome device which is specifically used for preparation of organic tissue specimens for microscopic investigations to an extra thin thickness required therefor. More specifically, this invention is conerned with improvements in a microtome knife sharpening machine including a specific supporting assembly for holding a microtome knife in angular relationship with respect to the grinding surface of a grinding wheel incorporated therein for sharpening microtome knives.

In consideration of the fact that a knife for a microtome device is specifically used for cutting processed organic tissue blocks for a microscopic investigation to such a thickness of the order ranging from I to 2 microns, and in addition, thus obtained specimens for microscopy should have as little deviation as possible from a predetermined cutting thickness, it is essential that such grinding or sharpening operation should be preformed with extremely high precision.

In general, such a sharpening machine known heretofore has been relatively complex in construction, and inevitably difficult or very delicate in its handling operation. Above all, since the supporting means for such a microtome knife of the above stated character should be precise in the angular setting and securing of the microtome knife with respect to the grinding surface as a reference surface in the grinding operation, it has generally been considerably troublesome and difficult to adjust such operating factors of the knife with respect to the grinding surface of the grinding wheel as angular setting, levelling, vertical positioning. etc. of the microtome knife, and to turn over the microtome knife in a proper condition from a state in which one edge surface of the knife contacts the grinding wheel to a state in which the opposite edge surface contacts the grinding wheel.

SUMMARY OF THE INVENTION It is therefore a primary object of this invention to provide an improved microtome knife sharpening machine which greatly facilitates several operations relating to the edge sharpening operation in a microtome knife sharpening machine.

It is another object of this invention to provide an improved microtome knife sharpening machine which includes an angularly adjustable supporting assembly for the microtome knife so that the microtome knife may selectively take a plurality of angular positions for facilitating such steps relating to the sharpening operation as overturning, replacement, checks, and hand correction work of the microtome knife in addition to the edge sharpening operation.

It is a further object of this invention to provide an improved microtome knife sharpening machine which affords provision of a relieved position of the microtome knife for the edge sharpening operation thereof, wherein the microtome knife is kept in a suitable angular position within a given angular range with respect to the grinding surface of the grinding wheel so that the knife may freely press under its own weight on the grinding surface at an optimum grinding angle.

It is a still further object of this invention to provide an improved microtome knife sharpening machine which affords as a secondary effect a self-dressing function of the grinding wheel during the edge sharpening operation.

It is a still further object of this invention to provide an improved microtome knife sharpening machine which affords visual and exact indication of fine move ments of the microtome knife during the edge sharpening operation in terms of unit dimension by using a dial indicator incorporated therein.

According to this invention, briefly summarized, there is provided an improved microtome knife sharpening machine of the type including a base structure, a grinding wheel rotatable about an axis and having a planar grinding surface, means for driving the grinding wheel in rotation, microtome knife carrier means, and support means mounted on the base structure to be swingable about pivot axis and supporting the microtome knife carrier means, whereby a microtome knife held by the carrier means is capable of being angularly adjusted with respect to the grinding surface, wherein there is provided an improvement which comprises rod means rotatably supported by the support means and being rotatable with the microtome knife carrier means about the pivot axis with respect to the support means, slidable means so mounted on the rod means that the same is not allowed to rotate relative to the rod means but is allowed to move axially relative to the rod means, first engaging means disposed on the slidable means, at least two second engaging means disposed on the base structure, the first engaging means being adapted to engage selectively with one of the second engaging means so as to enable the microtome knife means to take at least two angular positions selectively, and resilient means urging the slidable means and hence the first engaging means toward the second engaging means thereby to provide the tendency of the first engaging means moving into engagement with the second engaging means.

The nature, principle, and details of the present invention, as well as further objects and advantages thereof, will become more apparent from the following detailed description with respect to a preferred embodiment of the invention, when read in conjunction with the accompanying drawings, in which like parts are designated with like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a plan view, with some parts removed for clarity, showing a grinding wheel arrangement of a microtome knife sharpening machine of this invention;

FIG. 2 is a side elevational view, partly in vertical section, showing the microtome knife sharpening machine shown in FIG. 1',

FIG. 3 is a top plan view, partly in section and on an enlarged scale, showing a microtome knife support assembly of the sharpening machine shown in FIG. 2;

FIG. 4 is a fragmentary perspective view showing an end portion of a sleeve for angular adjustment of a microtome knife held by the support assembly of the sharpening machine;

FIG. 5 is a fragmentary view showing a reference wall surface with a plurality of depressions for angular adjustment of the microtome knife with respect to the grinding surface of a grinding wheel;

FIG, 6 is a top plan view, partly in section, showing a second example of the microtome knife support assembly;

FIG. 7 is an enlarged fragmentary side elevational view showing in detail the components of the microtome knife support assembly;

FIG. 8 is a fragmentary perspective view showing a dial gauge support arm of the microtome knife support assembly;

FIG. 9 is a perspective view showing a dial gauge operating strap of the microtome knife support assembly;

FIG. 10 is a fragmentary view, partly in section, showing the microtome knife held in a U-shaped knife holder of the microtome knife support assembly; and

FIG. 11 is a diagrammatic view showing a sharpening state of the microtome knife on the grinding surface of the grinding wheel.

DETAILED DESCRIPTION Description will now be given on a preferred embodiment of a microtome knife sharpening machine according to this invention in conjunction with the accompanying drawings.

Referring first to FIGS. 1 and 2, there is shown a microtome knife sharpening machine of this invention which includes a base 1, a journal box 2 disposed on the front portion of the base 1, a driving shaft 3 extending between the lateral end plates of the journal box 2 having an elongated slot along the length thereof, and a threaded shaft 4 extending in parallel with the shaft 3 between the lateral end plates and adapted to lead a grinding wheel assembly through threaded connection therewith, in both rightward and leftward directions as viewed in FIG. 1. On the shaft 3, there is secured a belt pulley 5 at the rightmost end thereof as viewed in FIG. 1, and a belt 50 is passed around the pulley 5 and a driving pulley on the output shaft of an electric motor 6. The above mentioned two shafts 3 and 4 are interconnected with each other by means of gears 7 and 8 secured to the shafts 3 and 4, respectively, so that the both shafts 3 and 4 are driven concurrently by the motor 6.

There is further provided a grinding wheel mount 9 on the upper surface of the journal box 2, which mount is slidable in rightward and leftward directions as viewed in FIG I in parallel with the above mentioned two shafts 3 and 4. The mount 9 has a projection 10 extending downwardly for thread engagement with the screw threads on the shaft 4 and a pair of spaced apart projections 11 disposed respectively in sliding contact with axial end faces of a worm 12 mounted rotatably with and axially slidably on the shaft 3 through a slide key provided radially in the central bore of the worm.

A grinding wheel 13 is secured to a vertical shaft 14 journaled in the mount 9, and to the lower end of the shaft I4, a worm wheel 15 is secured for engagement with the worm 12. Consequently, when the shafts 3 and 4 are driven in rotation by the motor 6, the grinding wheel mount 9 is caused to move along the shafts 3 and 4, while the grinding wheel 13 is caused to be driven in rotation through the worm wheel 15.

There is provided an electric switching arrangement for periodically changing the direction of rotation of the motor 6 and hence the direction of travel of the grinding wheel mount 9 along the shaft 3. A dog 16 is disposed on the front side of the mount 9 and alternately hit against limit switches I7 and 18 disposed in positions corresponding to the extreme points of the reciprocating travelling of the mount 9, so that the electric circuit for the motor 6 is changed-over and the direction of rotation thereof is reversed periodically. By this change-over operation, the grinding wheel mount 9 is caused to be moved on the journal box 2 in a reciprocating manner, while the grinding wheel 13 thereon is driven in rotation.

In FIG. 2, there is shown a stand 19 which is supported slidably on a bracket 20, the bracket extending laterally from the journal box 2 as viewed in FIG. 2, so that the stand 19 may be adjusted in its position relative to the grinding wheel 13. Further, there is mounted a microtome knife support member 21 on one side of the stand 19 in vertically slidable relationship therewith, by means of a dovetail tenon 19a (FIG. 3) of the stand 19 and a dovetail groove 21a provided in the vertical side of the stand 19 remote from the grinding wheel and engaging the tenon 19a, for permitting vertical movement of the microtome knife support member 21 with respect to the stand 19. There is provided a threaded rod 38 for thread engagement with a projection 39 extending from the support member 21 into the hollow interior of the stand 19, which threaded rod is designed for adjusting the vertical level of the support member 21 and is provided with a knob 38a at the top thereof for enabling manual turning thereof.

Now, referring to FIG. 3, the microtome knife support member 21 includes two supporting walls 22 extending outwardly from the front fact thereof, and these supporting walls 22 support a horizontal rod 23 extending therethrough and projecting to the left from the support member 21 as viewed in FIG. 3 in such a manner that the rod 23 can be rotated manually to a desired angular position with respect to the support member 21. Between the supporting walls 22, there is a carrier block 24 secured rigidly on the rod 23 and having an integral clamping section 240 on the central portion of which clamping section a knife holder 26 of generally U-shaped cross section is provided for securing rigidly a microtome knife 25 in a proper position for knife sharpening operation by using set screws 40.

There is a enlarged diameter portion 27 on the free end of the rod 23, the portion 27 having an outer diameter permitting an adjusting sleeve 28 to be slidably fitted thereonto. The sleeve 28 extends over the portion of the rod 23 projecting from the support member 21 in coaxial relationship therewith, and has a collar 29 rigidly secured to the inner wall thereof, the collar having a bore of a diameter to permit itself to be freely slid along the rod 23. Between the portion 27 and collar 29 there is interposed a compression coil spring 30, so that the spring may urge by its resilient force the collar 29 and thus the adjusting sleeve 28 against the support member 21. Since the adjusting sleeve 28 is slidably fitted on the portion 27 of the rod 23, the sleeve 28 may be moved manually in the axial direction.

In addition, there is provided an engaging arrangement comprising a pin 34 projecting radially outwardly from the enlarged diameter portion 27 and a slot 35 formed in the sleeve 28 in the lengthwise direction thereof and receiving the pin 34 therein so that the sleeve 28 can be manually moved in the axial direction without relative rotation thereof with respect to the rod 23. Also, there is an arm 32 provided rigidly with the sleeve 28 at the proximal end of the same and extending radially outwardly so as to selectively engage, by

means of a peg 31 projecting at the tip end thereof toward the support member 21 (see FIG. 4), with depressions 33a, 33b, 33c, and 33d formed in the lateral surface of the support member 21 in angularly spaced apart relationship along an arc of a circle having its center on the axis of the adjusting sleeve 28 or the rod 23 as shown in FIG. 5.

The above mentioned manual axial movement of the adjusting sleeve 28 with respect to the enlarged diameter portion 27 permits the peg 31 on the arm 32 to be disengaged from any one of the depressions 33a, 33b, 33c, and 33d for the purpose of angular adjustment of the microtome knife 25 held in the knife holder 26 in accordance with the angular positions of such depression. Among the depressions, the depression 33d is particularly of arcuate shape and extends over a certain angular range.

A clamping rod 36 is provided for releaseably securing the microtome knife holder 26 against rotating motion thereof with respect to the carrier block 24 about the axis of a shaft 37 extending integrally from the knife holder 26. The shaft 37 is rotatably fitted in the carrier block 24 and its clamping section 24a, and when the clamping rod 36 is manually turned in a tightening direction the shaft 37 is tightened and prevented from rotating. More specifically, the clamping section 240 formed integrally with the carrier block 24 is provided with a slit 41 cut along the shaft 37, and a screwthreaded tip end of the clamping rod 36 extends a portion thereof along an opening extending therethrough and adapted across the slit 4]. Therefore, the slit 41 can be narrowed, by manually turning the clamping rod 36 in the tightening direction, so as to cause the knife holder 26 to be secured rigidly in a desired angular position. It will be understood that the microtome knife held by the holder 26 is prevented from accidental rotating movements with its one edge surface set in grinding contact with the grinding surface of the grinding wheel 13.

With the arrangement described above, when the adjusting sleeve 28 is manually pulled outwardly in the direction as indicated by arrow A in FIG. 3 and the peg 31 is disengaged from any of the depressions 33a, 33b, 33c, and 33d against the biasing force of the compressed spring 30, the adjusting sleeve 28 and the rod 23 are released and permitted to effect free angular movement, and, consequently, the carrier block 24 secured to the rod 23, and hence the knife 25 can now be ready for manual angular adjustment with respect to the axis of the rod 23. In this connection, it is now possible to cause the peg 31 to be releasably engaged with any other depressions.

For instance, when the peg 31 is manually selectively caused to engage with the depression 33a, the knife holder 26 is held in a position where the microtome knife 25 is at the angle of 60 above the horizontal plane, and this position is particularly suitable for the manual overturning of the microtome knife, after the sharpening operation is completed on one side thereof, to sharpen the edge of the reverse side. For this manual overturning operation, the clamping rod 36 is loosened by turning it in the untightening direction to cause the slit 41 of the clamping section 24a to be widened. As a result, the knife holder 26 with the microtome knife 25 is allowed to undergo rotating movement with re spect to the axis of the shaft 37, and thus the overturning operation of the microtome knife can be performed easily without the necessity of detaching and then resetting the knife in position for the succeeding sharpening operation.

When the peg 31 is engaged with the depression 33b in the lateral side of the support member 21 after manually rotating the adjusting sleeve 28, the knife holder 26 takes a position 15 above the horizontal plane, which position is particularly provided for facilitating attachment or detachment of the microtome knife to and from the holder 26 before and after the sharpening operation. When the peg 31 is then set to engage with the depression 33c, it provides a horizontal position of the microtome knife wherein it is convenient to check the ground edge portion of the knife or to remove any burrs which are likely to be produced on the edge surface opposite to that surface just ground by the sharpening operation.

Now, when the peg 31 is set to engaged with the arcuate depression 33d, the knife holder 26 with the microtome knife 25 therein is kept in condition such that the microtome knife will swing within a range of angle 6 with respect to the axis of the rod 23 so as to press on the grinding surface of the grinding wheel 13 with a force due to gravity. In this condition, the microtome knife undergoes grinding contact with the grinding surface with a degree of freedom allowing the knife to be swung about the pivot axis of the rod 23 under its own weight.

It should be noted that during sharpening operation of the microtome knife under this condition, the microtome knife is caused to press on the grinding surface of the grinding wheel 13 under its own weight while being relieved from any positive force to compel the knife edge surface against the grinding surface. On the other hand, the contact angle of the microtome knife formed between the microtome knife and the grinding surface of the grinding wheel during sharpening operation can be adjusted finely by manually turning the knob 380, which is connected to the threaded rod 38 threadedly engaged with the projection 39 of the support member 21, to displace the member 21 vertically for adjustment of the microtome knife 25.

During the sharpening operation of the microtome knife by the grinding wheel of the machine, if the grinding surface of the grinding wheel 13 should not be definitely in parallel relationship with the edge surface of the microtome knife to be sharpened in the beginning stage of the operation, the grinding surface will wear-fit to the edge surface thereof as the grinding operation progresses, so that a self-dressing operation of the grinding wheel is effected.

With the above described improved microtome knife sharpening machine according to this invention, there are afforded various advantageous features. For example, it is practically possible to permit the microtome knife to be disposed selectively in one of several angular positions for convenience in such as the overturning step, checking step, and further hand correction steps for finishing procedure and the grinding position where the knife presses on the grinding surface of the grinding wheel within a given angular range. It is apparent that this provides considerable ease and convenience in the performance of the steps relating to the sharpening operation of the microtome knife. In FIGS. 6 through 11, there is shown a second example of the microtome knife support assembly according to this invention. Descriptions will now be given on only the differences of the second example from the first one described hereinbefore. Referring to FIGS, 6 and 7, there is provided a support bar 42 for a dial indicator 45 to be located above the upper surface of the support member 21, the support bar being secured to the member 21 by set screws 43. This support 42 is provided with a slit 44 at the leftmost end thereof as viewed in FIGS. 6 and 8 for receiving the dial indicator therein and clamping it rigidly by a screw 46 (FIG. 8). Also, there is a L-shaped contact strap 47 (FIG. 9) attached to the lower surface of the clamping section 240 of the carrier block 24 at one end thereof. The other end 470 of the contact strap 47 is disposed adjacent the position where the dial indicator is, and is in contact with the sensing tip 450 of the indicator 45.

Since the microtome knives are designed with several thickness, the knife holder 26 has an extra width of the opening thereof so that a knife of any thickness may be held in position in the holder 26 through a shim 48 of a suitable thickness by using set screws 40 as shown in FIG, 10. In this procedure, the knife 25 must be secured in the holder 26 with its edge line definitely lying on the reference center line 37a of the knife holder shaft 37. This arrangement is of significance, since, otherwise, the angular relationship of the microtome knife edge surfaces would be unduly asymmetrical with respect to the grinding surface of the grinding wheel 13, or in other words, the bevel angles 011 and a2 defined by the edge surfaces C and B of the microtome knife with respect to the reference line 37a cannot be identical. The correct setting position of a microtome knife 25 held by the knife holder 26 with respect to the grinding surface of the grinding wheel 13 is shown in FIG. 11.

With the arrangement of the microtome knife support assembly of this example, wherein the dial indicator 45 is mounted with its sensing tip 450 abutting the tip end 470 of the contact strap 47 which is secured to the lower part of the carrier block 24, when the microtome knife 25 is set in position for sharpening operation on the grinding surface of the grinding wheel 13 with one edge surface B of the knife resting thereupon, the contact strap 47 can swingably move about the axis of the rod 23 together with the knife holder 26 set in the sharpening position as the knife edge sharpening operation is carried out by the grinding surface of the grinding wheel. Even if the swinging motion of the knife holder 26 is very small in extent, it is immediately transmitted to the sensing tip 45a of the dial indicator 45 by the contact strap 47 as best seen in FIG. 7, and thus the dial indicator indicates the extent of such motion in terms of unit dimensions on the dial. Consequently, when the microtome knife 25 is turned over from the state in which its edge surface B contacts the grinding wheel to the state in which the opposite edge surface C contacts the grinding wheel, and if the edge line of the knife does not coincide with the reference line 37a of the shaft 37, the dial indicator reading will differ from the previous reading, indicating the amount of angular deviation in terms of unit dimensions on the dial. Thus, improper angular setting of the knife can be corrected. Through such dial reading, it can be determined how much dimensional compensation should be taken, whereby it is possible to replace the shim by another shim of a proper thickness, and this affords an optimum setting of the microtome knife 25 with respect to the grinding surface of the grinding wheel.

As described hereinabove, with the dial indicator incorporated in the knife support assembly of the microtome knife sharpening machine, it becomes possible to determine exactly whether or not the microtome knife 25 is properly positioned with respect to the reference center line of the knife holder 26, and consequently, the grinding angles a] and (12 defined by the edge surfaces of the knife can be definitely equalized. This means that the machine according to this invention can carry out edge sharpening operation of microtome knives with ease and high prescision.

I claim:

1. In a microtome knife sharpening machine comprising a base structure, a grinding wheel rotatable about an axis and having a planar grinding surface, means for driving said grinding wheel in rotation, microtome knife carrier means, and support means mounted on said base structure to be swingable about a pivot axis and supporting said knife carrier means, whereby a microtome knife held by the carrier means is capable of being angularly adjustable with respect to said grinding surface, the improvement which comprises:

rod means rotatably supported by said support means and being rotatable with said microtome knife carrier means about said pivot axis with respect to said support means;

slidable means so mounted on said rod means that the same is not allowed to rotate relative to said rod means but is allowed to move axially relative to said rod means;

first engaging means disposed on said slidable means;

at least two second engaging means disposed on said base structure, said first engaging means being adapted to engage selectively with one of said second engaging means thereby to enable said microtome knife carrier means to take at least two angular positions selectively; and

resilient means urging said slidable means and hence said first engaging means toward said second engaging means thereby to provide a tendency of said first engaging means to move into engagement with said second engaging means.

2. The improvement as claimed in claim 1 wherein said rod means is a pivot shaft extending outwardly from said support means along said pivot axis and supporting rigidly said knife carrier means, and wherein said slidable means is a sleeve extending on and along said pivot shaft, said pivot shaft having on one end thereof remote from said support means an enlarged portion of an outer diameter such that said sleeve may be slidably fitted thereon, said sleeve having a collar on the inner wall thereof at the end thereof adjacent said support means, whereby said pivot shaft and said sleeve are engaged with each with each other in coaxial relationship.

3. The improvement as claimed in claim 2 wherein said enlarged portion of said pivot shaft is further provided with a pin projecting radially outwardly therefrom, said sleeve being further provided with a longitudinal slot adjacent the end thereof corresponding to said enlarged portion, said pin being slidably engaged with said longitudinal slot whereby said sleeve can be slid axially relative to said pivot shaft without relative rotation therebetween.

4. The improvement as claimed in claim 2 wherein said first engaging means is a peg projecting from an arm extending radially outwardly from said sleeve at the end thereof corresponding to the position of said collar, and said second engaging means are at least two depressions formed in the lateral surface of said support means facing said arm, said peg being adapted to engage selectively with any one of said depressions under the resilient force of said resilient means.

5. The improvement as claimed in claim 4 wherein one of said depressions is an arcuate groove formed along an are having the center thereof on said pivot axis, said arcuate groove extending with an angular range such that, when said peg is in engagement therewith, said knife carrier means is within an angular range such that said microtome knife is in grinding contact with said grinding surface with a degree of freedom allowing said microtome knife to be swung about said pivot axis under its own weight.

6. The improvement as claimed in claim 2 wherein said resilient means is a coil spring extending between said enlarged portion of said pivot shaft and said collar of said sleeve and imposing resilient force upon said sleeve thereby to cause said first engaging means to be releasably engaged with any one of said second engaging means.

7. The improvement as claimed in claim 2 further comprising indicator means mounted on said support means and displacement transmitting means secured to said knife carrier means and extending to said indicator means to transmit the angular displacement of the carrier means to said indicator means.

8. The improvement as claimed in claim 7 wherein said transmitting means comprises a contact strap rigidly secured at one end thereof to said knife carrier means with the other end thereof extending for contact engagement with a sensing member of said indicator means in a fashion such that said contact strap can swing together with said knife carrier means and hence said microtome knife with respect to said pivot axis, whereby fine angular movements of said microtome knife with respect to said pivot axis are transmitted through said contact strap to said indicator means and sensed by the latter. 

1. In a microtome knife sharpening machine comprising a base structure, a grinding wheel rotatable about an axis and having a planar grinding surface, means for driving said grinding wheel in rotation, microtome knife carrier means, and support means mounted on said base structure to be swingable about a pivot axis and supporting said knife carrier means, whereby a microtome knife held by the carrier means is capable of being angularly adjustable with respect to said grinding surface, the improvement which comprises: rod means rotatably supported by said support means and being rotatable with said microtome knife carrier means about said pivot axis with respect to said support means; slidable means so mounted on said rod means that the same is not allowed to rotate relative to said rod means but is allowed to move axially relative to said rod means; first engaging means disposed on said slidable means; at least two second engaging means disposed on said base structure, said first engaging means being adapted to engage selectively with one of said second engaging means thereby to enable said microtome knife carrier means to take at least two angular positions selectively; and resilient means urging said slidable means and hence said first engaging means toward said second engaging means thereby to provide a tendency of said first engaging means to move into engagement with said second engaging means.
 2. The improvement as claimed in claim 1 wherein said rod means is a pivot shaft extending outwardly from said support means along said pivot axis and supporting rigidly said knife carriEr means, and wherein said slidable means is a sleeve extending on and along said pivot shaft, said pivot shaft having on one end thereof remote from said support means an enlarged portion of an outer diameter such that said sleeve may be slidably fitted thereon, said sleeve having a collar on the inner wall thereof at the end thereof adjacent said support means, whereby said pivot shaft and said sleeve are engaged with each with each other in coaxial relationship.
 3. The improvement as claimed in claim 2 wherein said enlarged portion of said pivot shaft is further provided with a pin projecting radially outwardly therefrom, said sleeve being further provided with a longitudinal slot adjacent the end thereof corresponding to said enlarged portion, said pin being slidably engaged with said longitudinal slot whereby said sleeve can be slid axially relative to said pivot shaft without relative rotation therebetween.
 4. The improvement as claimed in claim 2 wherein said first engaging means is a peg projecting from an arm extending radially outwardly from said sleeve at the end thereof corresponding to the position of said collar, and said second engaging means are at least two depressions formed in the lateral surface of said support means facing said arm, said peg being adapted to engage selectively with any one of said depressions under the resilient force of said resilient means.
 5. The improvement as claimed in claim 4 wherein one of said depressions is an arcuate groove formed along an arc having the center thereof on said pivot axis, said arcuate groove extending with an angular range such that, when said peg is in engagement therewith, said knife carrier means is within an angular range such that said microtome knife is in grinding contact with said grinding surface with a degree of freedom allowing said microtome knife to be swung about said pivot axis under its own weight.
 6. The improvement as claimed in claim 2 wherein said resilient means is a coil spring extending between said enlarged portion of said pivot shaft and said collar of said sleeve and imposing resilient force upon said sleeve thereby to cause said first engaging means to be releasably engaged with any one of said second engaging means.
 7. The improvement as claimed in claim 2 further comprising indicator means mounted on said support means and displacement transmitting means secured to said knife carrier means and extending to said indicator means to transmit the angular displacement of the carrier means to said indicator means.
 8. The improvement as claimed in claim 7 wherein said transmitting means comprises a contact strap rigidly secured at one end thereof to said knife carrier means with the other end thereof extending for contact engagement with a sensing member of said indicator means in a fashion such that said contact strap can swing together with said knife carrier means and hence said microtome knife with respect to said pivot axis, whereby fine angular movements of said microtome knife with respect to said pivot axis are transmitted through said contact strap to said indicator means and sensed by the latter. 